1. Field of the Invention
The present invention relates to an apparatus for manufacturing a curved sheet of glass, such as a three-dimensionally curved sheet of glass which is curved in both transverse and longitudinal directions, such as a front windshield for use on an automobile.
2. Description of the Prior Art
To manufacture a three-dimensionally curved sheet of glass which is curved in both transverse and longitudinal directions, it has been customary to use upper and lower molds (ring molds) for pressing a glass sheet therebetween to a desired shape.
However, an apparatus for pressing a glass sheet with upper and lower molds therebetween is complex in structure, and a three-dimensionally curved sheet of glass produced by such an apparatus is relatively expensive.
Another process of manufacturing a three-dimensionally curved sheet of glass is disclosed in Japanese laid-open patent publication No. 52-78226.
One known apparatus capable of successively producing three-dimensionally curved sheets of glass efficiently at a low cost employs an array of beds as disclosed in "Glass Handbook", page 491, edited by Sumio Sakuhana, et al. and published on Sep. 30, 1975 by Asakura Shoten.
Specifically, the known apparatus has a plurality of beds, each having a number of hot air ejection holes defined in an upper panel thereof. The beds are arranged successively horizontally within a heating furnace. A glass sheet is floatingly fed successively over the beds through the heating furnace. While the glass sheet is being fed in the heating furnace, it is heated and bent to the shapes of the upper surfaces of the beds.
For bending a glass sheet in a direction normal to the direction in which it is fed through the heating furnace, the upper surface of each bed may be shaped such that it is higher at its central region and lower at lateral sides thereof. However, forming a three-dimensionally curved sheet of glass for use as an automobile front windshield requires that the upper surface of each bed be curved in the direction of feed as well as in the direction normal thereto.
If the upper surface of each bed were curved in the direction of feed, then abrupt steps or surface interruptions would be created at the joints between the beds, and this would obstruct smooth feeding of glass sheets over the beds.